1. Field of the Invention
This invention relates to an expansion anchor capable of being expanded within a hole bored in a rigid material such as a stone and concrete by thrusting a lock plug into the inside of the anchor so as to fasten something else onto it or reinforce the rigid material.
2. Description of the Prior Art
There have been so far a variety of expansion anchors capable of being secured onto a rigid material such as concrete. One expansion anchor which is widely used is shown in FIG. 1 as one example. In principle, the anchor of this type comprises a cylindrical anchor body 1, a wedge plug 5 which is forced into the inside of the anchor body 1, and a threaded bolt 3 having a clamp nut 7 at one end portion thereof and brought into threaded connection with the wedge plug 5 at the other end portion. After inserting the anchor body 1 in a fitting hole bored in a concrete material or other rigid materials, the wedge plug 5 is forced into the anchor body 1 by turning the thread bolt 3 to thereby expand the anchor body. Thus, the anchor is fixedly secured within the concrete material in a non-removable state.
The anchor body of this expansion anchor is generally made of relatively soft material and has longitudinal expanding slits in its leading end portion so as to facilitate expansion of the anchor body by forcibly thrusting the wedge plug 5 into the anchor body 1. The anchor body thus expanded inside the hole in the concrete material comes into frictional contact with the inner surface of the concrete hole to be thereby kept in its non-removable state. In order to heighten the non-removable effect of the anchor, the anchor body is provided on its outer circumferential surface with checking steps 9 as illustrated. To further improve the non-removable effect of the anchor expanded within the concrete hole, the degree of expansion of the anchor body must be increased sufficiently.
However, an anchor capable of being sufficiently expanded requires a markedly large thrusting force to be imparted to the wedge plug 5. Moreover, this anchor is disadvantageous in that the frictional clamping force brought about by the checking steps 9 formed in the outer circumferential surface thereof is not sufficient to steadily secure the anchor in the concrete material. Also, the clamping force depends upon the diameter of the hole bored in the concrete material or the like relative to the outer diameter of the anchor body, and it is difficult to form the hole with a suitable diameter.